Conventional digital telecommunications switches often employ a time slot interchange (TSI) to effect switching using time division multiplexing (TDM) techniques. As known, a conventional TSI includes a memory device for storing digital information (i.e., voice, data, etc.), a counter and a control store. The counter cyclically generates consecutive addresses which are applied to the memory device. As each such address is applied to the memory device, a portion of digital information, known as a time slot (i.e., a byte) is stored in the location of the memory device corresponding to that address. In general, in prior art telecommunications switches each time slot is associated with a single, unique "port" of the switch, wherein each port represents a possible connection for a telephone line, trunk or other device.
The switching function is effected by the control store, which generates addresses simultaneously with the counter. However the addresses generated by the control store may be dynamically changed and are generally not consecutive. Thus, as these reordered addresses are applied to the TSI memory device during a read operation, the effect is to switch or interchange the order in which the previously stored information is retrieved from the memory device. In this fashion, information which is stored in the memory device after being received from any given port during a particular time slot may be subsequently read from the memory and transmitted to any other port during another time slot.
In addition to the basic time switching function just described, many digital telecommunications switches provide communications or call processing services. Such services typically include tone generation and tone detection, and other known services to meet the requirements of a particular system application.
A conventional technique for providing call processing services is to configure a switch with the necessary dedicated circuitry (e.g., one or more tone generators and one or more tone receivers of the appropriate protocols) and use the TSI to establish communication paths between such dedicated circuitry and the appropriate ports. For example, assume that a user lifts her handset and the switch detects that her line is now off-hook. The switch then responds by establishing a communication path through the TSI between an available tone generator and the off-hook line, and consequently, a dial tone produced by the tone generator is heard by the user.
There are, however, significant disadvantages with this conventional technique and a solution to those problems is articulately set forth in U.S. Pat. No. 5,349,579 entitled "Telecommunications Switch With Programmable Communications Services" (hereinafter the "'579 Patent"), assigned to the assignee of the present invention and incorporated herein by reference. Although the dynamic allocation of resources disclosed in the '579 Patent is a significant advancement in the state-of-the-art, the system disclosed therein switches or processes only whole time slots (e.g., an entire byte) of information. That is, during each time slot, pulse code modulated (PCM) data is written into and read from the TSI by the digital signal processing modules byte-per-byte. One aspect of this architecture is that only a single DSP can use each time slot. That is, even if a DSP wishes to use less than a byte of a time slot, the entire byte is effectively committed to the DSP. Therefore, several bits of the byte would not be used during the time slot.
With the emergence of digital wireless services and the expansive features available with these services, dedicating an entire time slot to a DSP may be inefficient if a number of the DSPs are using less than the entire byte of the time slot.